Avoid "ROM hack" sites that bundle malware with downloads. Always verify the hash (CRC32 or SHA-1) of your ROMs against the No-Intro database.
But what exactly goes into a high-quality archive, and how do you manage one without getting overwhelmed by thousands of files? gba rom collection archive
If you want, I can:
To play your GBA ROMs, you'll need an emulator. Here are some popular GBA emulators: Avoid "ROM hack" sites that bundle malware with downloads